Development of Oryzophagus oryzae (Costa Lima) in rice cultivars

ABSTRACT Insect-resistant cultivars are essential for improving the management of pests such as Oryzophagus oryzae (Coleoptera: Curculionidae), which significantly decreases flooded rice yields. However, the degree of benefit brought to the crop varies with the type of resistance. This study aimed to evaluate the resistance of rice cultivars to O. oryzae, inferring about antixenosis and antibiosis effects on the development of larvae and adults. Under natural infestation conditions, a biennial experiment was carried out using a latin square design, with six treatments (cultivars) and plots with 30 plants (five rows of six plants equidistant 20 cm) irrigated with water depth of 15 cm. The number and weight of larvae by size, as well as the number, weight, emergence rate, and sex ratio of adults, were evaluated using standard soil, plant and root samples. Except for adult sexual ratio, the cultivars differed (p ≤ 0.05) for the other variables, whose relationship evidenced antibiosis effects at the larval stage, making possible to conclude that: the BRS Firmeza cultivar has resistance to O. oryzae due to antixenosis and/or antibiosis effects; BRS Ligeirinho is susceptible to this insect species, resulting in a relatively higher number of well-developed larvae and adults; and IRGA 417 shows an antibiosis action, restricting the adult emergence rates. The weight of adults gives a greater accuracy to the evaluation of the harmful effects of rice cultivars on the O. oryzae development.